1. Field of the Invention
The present invention relates to a piston-type quantity meter including a metering chamber having a bottom, a cylindrical chamber shell, a cover, a central journal, a guide ring, a separation wall located in a chamber interior, two inlet opening formed, respectively, in the chamber bottom and the chamber cover, and a radial outlet opening formed in the chamber shell; and an annular piston located in the chamber interior and having a cylindrical piston skirt, a piston cap, piston journal means, guide slot means formed in the piston skirt and corresponding to a width of the separation wall for pinning the piston on the separation wall, and radial outlet opening associated with the outlet formed in the chamber shell.
2. Description of the Prior Art
Piston-type quantity meters, which belong to volume meters, are well known and are disclosed, e.g., in U.S. Pat. No. 5,773,718 and International Publication WO93/22631. The known quantity meters, have a metering chamber through which an entire amount of fluid is forcefully flown. At that, a portion of a potential energy of a to-be-measured fluid is lost for driving the meter. The resulting pressure reduction is designated as a pressure loss as delta p. It results from deviations of the fluid flow path, cross-sectional changes along the flow path, from driving the annular piston of the meters, ets. . . .
In the metering chamber, an annular piston is arranged which during the measuring process, is displaced from a high pressure side to a lower pressure side. This displacement takes place automatically as a result of flow of the fluid through the meter. During rotation of the piston, two different volumes having, respectively, the same predetermined value are transported. During the transportation, the annular piston internal journal rotates about the central journal of the metering chamber.
The skirt of the annular piston is slotted over its entire height. The slot reciprocate once along a separation wall provided in the metering chamber with each revolution of the piston. The advantage of the oscillating movement of the piston consists in that the piston automatically returns into its initial position without any additional control elements, valves, slides, ets. . . .
The annular piston has, an upper journal for supporting a driver which transmits the rotary movement of the journal to a counter. A piston-type quantity meter of the above-described type is disclosed in a publication of Orlicek et al., xe2x80x9cZur Technik der Mengenxe2x80x94un Durchflussmessung von Fluxcex2ssigkeitenxe2x80x9d (Technik for measuring volume and flow rate of fluids), R. Oldenbourg Verlag, Munchen-Wien, 1971, p.p. 44-57.
In one type of piston quantity meters, an inlet opening is provide in both the bottom and the cover of the metering chamber, with a half of the volume of the to-be-measured fluid passing through each inlet opening. Rectangular slots, which are formed in the chamber shell and in the annular piston skirt, form outlet openings. With this flow of fluid through the metering chamber, in an ideal case, the axial flow forces acting on the piston are automatically balanced. See French Patent Publication FR-A 454609, article of Orlicek et al. xe2x80x9cZur Technik der Mengen-und Durchflusmessung von Fluessigkeiten,xe2x80x9d R. Oldenbourg Verlag, 1971, p.p. 44-57, and WO93/22631 (FIGS. 9 and 10).
Because in this type of piston-type quantity meters, the axial forces, which act on the piston, are automatically balanced, the meters of this type should have a greater measurement accuracy than the meters of the first two types. Actually, opposite is the case. The greater measurement inaccuracy of the piston-type quantity meters of this type is caused by formation of slits between the piston and the rectangular slot formed in the chamber shell and between the guide ring and the rectangular slot formed in the piston, respectively. Because of these slots the guide ring and the piston skirt, respectively, could not perform their sealing functions. Therefore, when the piston and the guide ring reach the respective slots, a noticeable increase of the effective slot width takes place, and this leads to a high slit leakage. For this reason, the piston-type quantity meter of this type could not be used up to the present.
Accordingly, an object of the present invention is to reduce the measurement error in the piston-type quantity meters with outlet slots formed in the chamber shell and the piston skirt.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a seal strip for sealing at least one of a slit formed between a chamber edge, which is defined by an intersection between a side wall of the outlet opening formed in the chamber shell and an inner wall of the chamber shell, and a piston edge, which is defined by an intersection between a side wall of the outlet opening formed in the piston skirt and an outer surface of the piston, and a second slot formed between a piston edge, which is defined by an intersection between a side wall of the outlet opening formed in the piston skirt and inner wall of the piston, and an outer wall of the guide ring.
According to the present invention, the seal strip can be secured, for sealing the outer slit, either to the chamber shell, projecting into the outlet opening formed in the piston skirt, or to the piston skirt, projecting into the outlet opening formed in the chamber shell.
The seal strip can be formed integrally with an element to which it is secured by being molded thereon.